It is a smaller barrel also made of tungsten, adn used for ballancing dart weight. The billet/barrel is also tapperd 2BA threads, some of which are both female ends, and some is one end male one end female. They are newly-developed type, made to different weights, popularly 1.0~5.0gram to balance different darts’ weight. Same size and content as tungsten barrels are used for such weights, see here below. dia. 1/4, 17/64, 9/32, 5/16 (inch); length 1.5, 1.6, 1.7, 1.75, 1.8, 1.9, 2.0, 2.15 (inch) 65%W barrels & billets; 70%W barrels & billets; 80%W barrels & billets; 85%W barrels & billets; 90%W barrels & billets;; 95%W barrels & billets;